Radioactive labeling of proteins using tritium is a very important technique used in neurological research to identify, isolate, and investigate the expression of proteins in biological systems. It is often necessary to use tritium as a radiolabel for this work because tritium in vivo labeled proteins retain their conformal structure and are suitable for binding assays. Currently, many tritium-labeled binding assays are done using inconvenient, time consuming, and expensive techniques involving scintillation cocktail measurement because no reliable and sensitive tritium detector is available to quantify the radioactivity directly and non-destructively from the sample. We propose to develop a novel solid-state based detector system capable of measuring the spatial activity distribution of tritiated biological specimens without the use of labor intensive liquid scintillation fluid techniques. This system is based on a large area array of silicon drift photodiodes which will be capable of directly sensing the low energy radiation emissions of the tritium-labeled samples collected on filter paper. A system based on the parallel acquisition of many such pixel elements would provide superior sample throughput for a wide variety of tritium-binding assays and thus will represent a significant productivity increase for many procedures while greatly reducing the quantity of chemical and radioactive waste that is generated. PROPOSED COMMERCIAL APPLICATION: The unique capabilities of the proposed silicon drift photodiode sensor will find many uses in the field of biological research where the need for position-sensitive counting or imaging of low-energy beta emitters such as (3)II, (14)C, (35)S, and (32)P would be an asset. The proposed sensor would greatly simplify and speed up assay procedures utilizing radioactive labels, and eliminate the radioactive liquid wastes produced using 'scintillation cocktails'.